(1) Field of the Invention
The present invention relates to a data storage array apparatus consisting of multiple data storage devices and provided with redundant data to improve reliability.
(2) Description of the Related Art
Conventionally, data storage array apparatuses (hereafter abbreviated as “array apparatus”) are used for increasing speed for data access and improving reliability by distributing data with redundancy over multiple hard disks.
The array apparatuses are well-known as Redundant Array of Inexpensive Disks (RAID). In the RAID-3, for instance, the storage area of each hard disk is divided into a plurality of blocks. Data is divided using the striping method and recorded onto the plurality of blocks, each of which forms a group together with corresponding blocks in the other hard disks including one that is exclusively used for storing parity data. The parity data is normally generated by carrying out the Exclusive-OR between the data blocks other than the parity block for each group.
Should one block of a group include corrupt or invalid data, the array apparatus refers to the parity data and the normal block data in the group to regenerate the normal data of the corrupt or invalid data and overwrite the same.
The array apparatus described in the U.S. Pat. No. 5,581,690 discloses technology for recording status information (error information), which indicates the existence of corrupt or invalid data in each block of each hard disk, on one of the hard disks, so that the use of corrupt or invalid data is prevented. That is, this array apparatus records the status information on the hard disk at each write operation of data and checks the status information immediately before each read operation. If corrupt or invalid data is not included, the apparatus reads the data. If corrupt or invalid data is included, the apparatus regenerates the block in the group.
In the above-described conventional technology, however, there is a problem of increase in a load for performing a write operation of the error information to a disk or a nonvolatile memory, because the size of the error information is increased to on the order of megabytes as storage capacity of hard disks and data transfer rate are increased.
For example, when writing material data for digital broadcast, such as Digital Video (DV) data, from the outside to the array apparatus in real time or sequentially, there is a problem that the write operation cannot be performed in real time or the delay occurs. This is because a write operation of data and parity data to a block to a group is necessarily followed by a write operation or an update operation of error information to disks or a nonvolatile memory, so that the ratio of this write or update operation occupying a bus is increased, which reduces the time for allowing the write operation of the material data to occupy the bus.